Groundwater Heat Pump (Water-to-Water)

A heat pump using groundwater as its source — the highest efficiency of any heat pump type (SPF 4.5-5.5), drawing on a constant groundwater temperature of around 10 °C.

How does a groundwater heat pump work?

A groundwater or water-to-water heat pump uses groundwater as its heat source. Groundwater is extracted via an abstraction well and passed through a plate heat exchanger, which removes a few kelvin of heat from it. The cooled water is returned via an injection well, downstream in the direction of flow, into the same aquifer. The heat pump raises the recovered heat to heating temperature via the refrigerant circuit. The great advantage: groundwater has an almost constant temperature of about 10 °C all year round. The temperature lift therefore remains small even in winter, and the seasonal performance factor (SPF) reaches 4.5 to 5.5 – considerably more than brine-to-water (4.0 to 4.5) or air-to-water (3.0 to 4.0). In summer, the groundwater can also be used for passive cooling.

Which buildings are suitable for a groundwater heat pump?

A productive aquifer is a prerequisite: at least 1.5 m³/h of water is needed per 10 kW of heating output, which must be verified by a pumping test. The water quality must be suitable; high iron or manganese content leads to ochre clogging of wells and heat exchanger. In Austria, a water rights permit under the Water Rights Act (Wasserrechtsgesetz) is required, which presupposes a pumping test, water analysis and usually a hydrogeological report. Drinking water protection zones and aggressive groundwater are exclusion criteria. Typical buildings are detached houses and apartment buildings in suitable regions – such as river valleys with gravel aquifers – as well as hotels, office buildings and industrial buildings with high, year-round heating and cooling demand.

What does a groundwater heat pump actually deliver?

Final energy falls by 75 to 85 %, CO2 emissions by more than 90 %. An office building with a heat demand of 150,000 kWh saves around 151,700 kWh of final energy and about 26 t of CO2 per year compared with a gas boiler. The investment for a detached house is 35,000 to 55,000 € including two wells; for office buildings, 1,800 to 2,800 € per kW of heating output. The higher costs compared with other heat pump types are offset by the best seasonal performance factor: over a 20-year service life, payback is 10 to 15 years.

Energy carrier

Erdgas, Heizöl → Strom

Savings potential

75-85 % Endenergie, >90 % CO2

Worked example

An office building with 1,500 m² of usable floor area has an annual heat demand of 150,000 kWh for heating and hot water. Until now, a gas boiler with an efficiency of 0.82 has covered this demand, consuming around 183,000 kWh of natural gas. The building is located in a river valley with a productive gravel aquifer; a pumping test confirms the required water volume, and the water rights permit is granted. Thanks to the constant groundwater temperature, the new water-to-water heat pump achieves a seasonal performance factor of 4.8. The final energy saving is calculated as 150,000 × (1/0.82 − 1/4.8) = 150,000 × (1.220 − 0.208) = 150,000 × 1.011 = 151,700 kWh per year. The heat pump's electricity consumption is only around 31,250 kWh. Comparing the emission factors of natural gas (0.201 kg/kWh) and the Austrian electricity mix (0.156 kg/kWh) gives a CO2 saving of about 26 t per year.

Investment & payback

EFH inkl. 2 Brunnen: 35.000-55.000 €; Bürogebäude pro kW: 1.800-2.800 €/kW Heizleistung · Service life: 20 a · Payback: 10-15 (höhere Investition wird durch Top-JAZ kompensiert) a

Applicability

Requirements

Exclusion criteria

Typical buildings

Frequently asked questions

How much does a groundwater heat pump cost?

A groundwater heat pump costs 35,000 to 55,000 € for a detached house including abstraction and injection wells, and 1,800 to 2,800 € per kW of heating output for office buildings. It is therefore more expensive than air-to-water or brine-to-water systems, but with a seasonal performance factor of 4.5 to 5.5 it achieves the lowest operating costs of all heat pump types. Over a 20-year service life, payback is 10 to 15 years.

Do you need a permit for a groundwater heat pump in Austria?

Yes, in Austria a groundwater heat pump requires a water rights permit from the district authority (Bezirkshauptmannschaft) or municipal authority (Magistrat) under the Water Rights Act. The procedure generally requires a pumping test, a water analysis and a hydrogeological report; the technical basis is VDI 4640 and ÖWAV Guideline 207. The permit usually includes conditions on abstraction volume, return temperature and monitoring.

What is the difference between a groundwater heat pump and a ground source heat pump?

A groundwater heat pump extracts groundwater directly via wells and uses its constant temperature of about 10 °C; it achieves a seasonal performance factor of 4.5 to 5.5. A ground source heat pump (brine-to-water) circulates an antifreeze mixture in closed borehole probes or ground collectors and achieves 4.0 to 4.8. The groundwater variant is more efficient but requires a productive aquifer, suitable water quality and a water rights permit.

How much water does a groundwater heat pump need?

A groundwater heat pump needs at least 1.5 m³/h of groundwater per 10 kW of heating output. For a detached house with 10 kW, that is around 1.5 m³/h; for an office building with 80 kW, about 12 m³/h. Whether the aquifer can deliver this volume permanently is verified by a pumping test lasting several days. The distance between abstraction and injection wells must be large enough to prevent the returned cold water from short-circuiting.

What problems can occur with groundwater heat pumps?

The most common problem is ochre clogging: iron and manganese compounds in the groundwater deposit in wells and heat exchanger, reducing yield and efficiency. A water analysis before planning and an intermediate circuit with a separating heat exchanger prevent this. Other risks are declining yield, sand ingress and permit conditions. Regular well maintenance and monitoring of flow rate and temperatures keep the system reliable for over 20 years.

Related measures

Standards & sources

Metering points in the EDM Toolbox

Empfohlene Messpunkte: Stromzähler WP, Wärmemengenzähler (Heizkreis + ggf. Quellseite), Brunnentemperatur (Saug+Schluck), Brunnen-Volumenstrom. So lässt sich JAZ und Quellergiebigkeit monitoren - wichtig für Bewilligungsauflagen.

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